BRANDON, South Dakota (CNN) -- Sen. Hillary Clinton said Friday that she regretted comments that evoked the June 1968 assassination of Robert Kennedy as part of her explanation for why she was staying in the presidential race late into the primary season.

Sen. Hillary Clinton apologized for comments made to a newspaper on Friday.

Earlier Friday afternoon, she told the editorial board of the Sioux Falls, South Dakota, Argus Leader that "My husband did not wrap up the nomination in 1992 until he won the California primary somewhere in the middle of June, right? We all remember Bobby Kennedy was assassinated in June in California. I don't understand it," she said.

Clinton complained that "people have been trying to push me out of this ever since Iowa" and said that position "historically ... makes no sense."

Later at an event in Brandon, South Dakota, she said, "Earlier today, I was discussing the Democratic primary history and in the course of that discussion mentioned the campaigns that both my husband and Sen. Kennedy waged in California in June in 1992 and 1968, and I was referencing those to make the point that we have had nominating primary contests that go into June. That's a historic fact." Watch more of Clinton's comments to the editorial board »

"The Kennedys have been much on my mind in the last days because of Sen. [Edward] Kennedy, and I regret that if my referencing that moment of trauma for our entire nation and particularly for the Kennedy family was in any way offensive. I certainly had no intention of that whatsoever," Clinton added. Watch Clinton explain her remarks »

During an interview with Radio Isla Puerto Rico on Saturday, Obama reacted to the Clinton comment.

According to a quote released by the campaign, he said, "I have learned that when you are campaigning for as many months as Sen. Clinton and I have been campaigning, sometimes you get careless in terms of the statements that you make, and I think that is what happened here. Sen. Clinton says that she did not intend any offense by it, and I will take her at her word on that."

On Friday, the campaign said in a statement, "Sen. Clinton's statement before the Argus Leader editorial board was unfortunate and has no place in this campaign."

Her campaign first defended the remarks, saying the New York senator had been making a historical parallel.

"She was simply referencing her husband in 1992 and Bobby Kennedy in 1968 of historical examples of the nominating process going well into the summer. Any reading into it beyond that is inaccurate and outrageous," Clinton spokesman Mo Elleithee said.

Kennedy, the brother of slain President John F. Kennedy, was shot and killed just moments after claiming victory in the California primary in 1968.

Friday night, Kennedy's son, Robert Kennedy, Jr., released a statement that said he understands the point Clinton was making and said it would be a mistake to be offended.

"I have heard her make this reference before, also citing her husband's 1992 race, both of which were hard-fought through June," he said. "I understand how highly charged the atmosphere is, but I think it is a mistake for people to take offense."

Also Friday, the Clinton campaign released a statement from Randell Beck, the newspaper's executive editor, saying Clinton was answering a question about whether her continued campaigning threatens party unity so close to the Democratic convention.

"Her reference to Mr. Kennedy's assassination appeared to focus on the timeline of his primary candidacy and not the assassination itself," Beck said in the statement.

Clinton's campaign manager, Maggie Williams, told CNN's Wolf Blitzer that people may have "misinterpreted what she meant."

"It was clear to anybody watching her this afternoon that she was ... deeply regretful, and people did not understand the context in which she made this reference, and so I think that she immediately, as soon as she could, spoke out to express her regret for ... perhaps the way that she had spoken or the people had misinterpreted what she meant," Williams said.

Clinton made a similar reference to Robert Kennedy in a March interview with Time magazine Managing Editor Richard Stengel, saying she could not envision a scenario in which party leaders would step in and call for the race to end.

"I think people have short memories," she said then. "Primary contests used to last a lot longer. We all remember the great tragedy of Bobby Kennedy being assassinated in June in L.A. My husband didn't wrap up the nomination in 1992 until June. Having a primary contest go through June is nothing particularly unusual."

All three candidates have Secret Service protection.

Clinton, the former first lady, has had agents guarding her since her husband's administration; Obama was assigned a protective detail in May 2007; and presumed Republican nominee Sen. John McCain agreed to accept Secret Service protection in April.